Merge #16561: tests: Use colors and dots in test_runner.py output only if standard output is a terminal

37f2784952cb6f598f82922f9ce71d40c9d74e26 tests: Use colors and dots in test_runner.py output only if standard output is a terminal -- allows for using the test runner output as input to other programs (practicalswift)

Pull request description:

  Use colors and dots in `test_runner.py` output only if standard output is a terminal -- allows for using the test runner output as input to other programs.

  I found the need for this when parsing `test_runner.py` output while investigating intermittent functional test failures.

  Before:

  ```
  $ test/functional/test_runner.py wallet_hd.py > output 2>&1
  $ less output
  Temporary test directory at /tmp/test_runner_₿_🏃_20190807_074115
  ESC[1mWARNING!ESC[0m There is already a bitcoind process running on this system. Tests may fail unexpectedly due to resource contention!
  Remaining jobs: [wallet_hd.py]
  .......................................^M                                       ^M1/1 - ESC[1mwallet_hd.pyESC[0m passed, Duration: 20 s

  ESC[1mTEST         | STATUS    | DURATION

  ESC[0mESC[0;32mwallet_hd.py | ✓ Passed  | 20 s
  ESC[0mESC[1m
  ALL          | ✓ Passed  | 20 s (accumulated)
  ESC[0mRuntime: 20 s
  ```

  After:

  ```
  $ test/functional/test_runner.py wallet_hd.py > output 2>&1
  $ less output
  Temporary test directory at /tmp/test_runner_₿_🏃_20190807_074244
  1/1 - wallet_hd.py passed, Duration: 20 s
  WARNING! There is already a bitcoind process running on this system. Tests may fail unexpectedly due to resource contention!
  Remaining jobs: [wallet_hd.py]

  TEST         | STATUS    | DURATION

  wallet_hd.py | ✓ Passed  | 20 s

  ALL          | ✓ Passed  | 20 s (accumulated)
  Runtime: 20 s
  ```

ACKs for top commit:
  laanwj:
    ACK 37f2784952cb6f598f82922f9ce71d40c9d74e26

Tree-SHA512: f15d95f9e07de2954c326d63d7a4bcd2971faeaa00386600dec2fb915ec89475aeef1dbc968b2c12aa5e988d4b3ed1974d6da0b6a3f1e1a105cfd90e8cb97cf6

0 files changed, 0 insertions, 0 deletions